The invention relates to photo-medical devices, and more particularly, to photo-medical devices that use radiation to detect structures.
Heart attacks are a major cause of death, disability, and health-care expense in the U.S. and other industrialized societies. Convincing new clinical data demonstrates that the rupture of non-occlusive, vulnerable plaques causes the majority of heart attacks. It has become increasingly evident that although hard plaque may produce severe obstruction in the coronary arteries, it is often the less prominent, asymptomatic soft vulnerable plaques that are prone to rupture.
The majority of vulnerable plaques are pools of lipid covered by a thin fibrous cap. The rupture of a vulnerable plaque releases this stored lipid into the blood. This initiates a chemical chain reaction that often culminates in the formation of a large blood clot in the coronary artery. The blood clot deprives the heart muscle of blood, and hence oxygen. The eventual result of this oxygen deprivation is a heart attack.
Because the lipid pool of a vulnerable plaque is covered, it cannot easily be seen by visible light. In addition, because the lipid pool tends to grow radially outward into the blood vessel, it does not significantly constrict blood flow. As a result, it is not readily detectable in an angiogram.
Ultrasonic waves have been used to detect vulnerable plaques. However, the level of detail, or resolution, is generally insufficient for accurate diagnosis. In addition, bombardment of the thin fibrous cap by sound waves can potentially trigger a rupture.
Magnetic resonance imaging (MRI) has also been used to detect vulnerable plaques. However, MRI requires long exposure times and are therefore not suitable for detecting moving structures. As a result, attempts to detect plaques in moving structures, such as coronary arteries, often result in blurred images.
Infrared light is known to penetrate short distances into the vascular wall and can therefore be used to detect such plaques as well as other subendothelial pathology. A difficulty associated with use of infrared radiation to detect vulnerable plaques is that a significant fraction of the incident infrared radiation is reflected from the inner wall. Only a small portion of this incident infrared radiation penetrates into the inner wall. Of this small portion, a still smaller portion emerges again from behind the inner wall. This portion must be separated from the infrared radiation reflected from the wall.
The invention is based on the recognition that when attempting to observe a structure that lies on another side of an interface between two media, it is often advantageous to illuminate the structure from one direction while simultaneously observing it from another direction. This enables one to observe the structure without the glare of specular reflection of radiation from the illumination source.
The underlying physical principle of the invention, will be apparent to anyone who has attempted to observe an object underwater on a dark night. If one were to shine a flashlight into the water and stand directly above the flashlight, all one would see would be the reflection of the flashlight from the waters surface. Any light returning from the object of interest would be overwhelmed by the brilliance of the glare. In contrast, if one were instead to look into the water along a different path than that followed by the beam of the light, one would be able to observe underwater objects illuminated by the flashlight, essentially by side-stepping this glare. However, if the path were too different, for example if one were observing from a point inches above the water surface, one would no longer be able to see underwater. This suggests the existence of an optimal path for observing underwater structures (i.e., structures on the other side of a boundary between two media).
In one embodiment, the invention includes first and second optical-redirectors mounted on a catheter. The first optical-redirector couples radiation between itself and a target along a first path. The second optical-redirector couples radiation between itself and the target along a second path. Either the first or second optical-redirectors, or both, can include a steering mechanism for selecting the first and/or second path.
In another embodiment, the invention provides a conduit having a longitudinal axis extending between a proximal portion and a distal portion. First and second waveguides extend between the proximal portion of the conduit and the distal portion of the conduit. These waveguides guide radiation longitudinally along the conduit. First and second optical-redirectors are in communication with the first and second waveguides respectively. These optical-redirectors are oriented to direct radiation along first and second paths extending between the first and second waveguides and a target.
In one aspect of the invention, the first optical-redirector comprises a conical surface having a cone axis parallel to the longitudinal axis of the conduit, the conical surface having a flare angle relative to the cone axis. The conical surface comprises a truncated half-cone or a truncated cone.
Various other optical-redirector designs are within the scope of the invention. For example, the first optical-redirector can re-direct radiation either by reflection or by refraction. The first optical-redirector can also be integrated into the first waveguide. This can be achieved, for example, by providing the first waveguide with a distal face having a surface normal vector with a radial component. Radiation traveling along the first waveguide can then reflect off the distal end and proceed sideways, or radially, out of the waveguide and onto the target. Conversely, radiation from the target can enter the waveguide, reflect off the distal end, and travel down the waveguide.
The first and second optical-redirectors can be on two discrete structures. Alternatively, the first and second optical-redirectors can be integrated into a single structure. For example, a single reflecting structure may have two facets, one of which is coupled to the first waveguide and the other one of which is coupled to the second waveguide.
Either the first or second optical-redirectors, or both, can include a steering mechanism, such as an actuator coupled to the optical-redirector. Where the optical-redirector includes a conical surface, the actuator can be configured to change the flare angle of the conical surface. Alternatively, the actuator can be configured to translate the optical-redirector along the longitudinal axis.
An actuator for changing the flare angle of a conical surface can be an inflatable balloon coupled to the conical surface. In this case, a change in volume of the balloon controls the flare angle of the conical surface. The actuator can also be a translating member coupled to the conical surface so that translation of the translating member controls the flare angle.
The first path can also be controlled by changing the position of the first and/or second optical-redirector along the longitudinal axis. In this aspect of the invention, the actuator includes a control wire coupled to the conical surface for translating the conical surface along the longitudinal axis.
One type of conical surface whose flare angle can be changed is made up of several reflecting panels. Each reflecting panel has a base end, and a free end longer than the base end. Each reflecting panel is pivotable about the base end between a closed position and an open position. Adjacent reflecting panels can overlap such that when each reflecting panel is pivoted to its open position, the plurality of reflecting panels forms a continuous reflecting surface.
Control of the first and second paths can be manual or automatic. In an embodiment in which automatic control of the first and second paths is available, a feedback loop can move the first optical-redirector relative to the second optical-redirector on the basis of a signal received from at least one of the first optical-redirector or the second optical-redirector. Such a feedback loop can include a detector in communication with the second waveguide, a motor in communication with the first actuator, and a processor in communication with the detector and with the motor. The processor is configured to drive the motor in response to a signal received from the detector.
Another aspect of the invention includes directing illuminating radiation along a first path extending between the catheter and the target, and collecting re-entrant radiation from the target along a second path extending between the target and the catheter. Reentrant radiation received from the target can then be analyzed to detect a structure on or in the target. In one aspect of the invention, the first and/or second paths are selected to enhance recovery of the re-entrant radiation.
As used herein, the term optical-redirector is used to describe a structure that couples radiation between a guiding structure and free space. The term waveguide refers to any such guiding structure. A conduit refers to any structure for providing a mechanical framework for mounting the various other elements of the invention so that they can be delivered to a target. The conduit includes catheters, endoscopes, and similar instruments.
Unless otherwise defined, all other technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.